1. Field of the Invention
The present invention relates to a compound semiconductor film, a light emitting film, a manufacturing method thereof.
2. Description of the Related Art
Various materials of a compound semiconductor containing three or more constituent elements (multi-element compound semiconductor) have been known up to now. The synthesis of the compound semiconductor, the production of a single crystal thereof, and the measurement of various physical properties thereof have been done. In recent years, in order to apply the compound semiconductor to devices, thin film technologies have been under active research. This greatly depends on the improvement of controllability of a thin film composition resulting from advances of thin film forming methods and apparatus technologies and on the advances of analysis methods and analysis technologies for formed thin films. An example of the devices developed under such circumstances is a thin film solar battery technology as disclosed in Japanese Patent Application Laid-Open No. H08-102546.
When a compound semiconductor film is used to manufacture a device, a manufacturing temperature of the device becomes a problem. When the manufacturing temperature is too high, not only a substrate material and films to be laminated are limited but also a special manufacturing apparatus and a special treatment apparatus are required.
In recent years, light emitting devices with high-intensity light emission have been under active development. The advance of technical development for an LED, an LD, an inorganic EL device, and an organic EL device is remarkable. In the case of the LED and the LD, electrons and holes are injected to the pn-junction of a semiconductor having a high-quality crystal structure to cause recombination light emission. In the case of the inorganic EL device, a high electric field is applied to an insulating phosphor thin film to cause light emission by electric field excitation of the light emission center of the phosphor thin film due to hot electrons. In the case of the organic EL device, a light emitting layer, an electron transporting layer, and a hole transporting layer, which are comprised of organic molecules or is a polymer thin film, are laminated. The light emission of excitons localized on the organic molecules is caused with recombination energy of the injected electrons and holes.
A MIS diode structure made of Al/ZnS/CuGaS2, serving as a direct current driven light emitting device using a chalcopyrite compound semiconductor, is disclosed in “Japanese Journal of Applied Physics 31, L1606, 1992”. According to this diode structure, electrons are injected through a Schottky barrier between a metal layer and an insulating layer, so green light, albeit weak, is emitted from a semiconductor layer. A structure is disclosed in “Journal of Physics and Chemistry of Solids 66, 1868-2005”, in which a heterojunction diode is obtained by laminating a p-type CuGaS2 chalcopyrite compound semiconductor layer and an n-type ZnO:Al compound semiconductor layer and is sandwiched between metals having different work functions. Attempts have been made to apply this structure to the direct current driven light emitting device. However, only weak light can be emitted at present.
The chalcopyrite compound semiconductor employed in the above structures is manufactured using an advanced manufacturing method such as a single crystal manufacturing method or an organic metal vapor phase epitaxy method, because higher p-type conductivity is required. It is necessary to manufacture the chalcopyrite compound semiconductor employed in the above structures at a temperature higher than 600° C.
A compound semiconductor which is represented by a Cu2—Zn—IV—S4 type (the Group IV element is selected from the group consisting of Sn, Ge, and Si) is disclosed in “Journal of Materials Science 40 (2005) 2003-2005” and the crystal structure and band gap (Eg) thereof are described as illustrated in FIG. 5. However, no description is found on the electrically conductive property. According to the description of “Solar Energy Materials & Solar Cells 75 (2003) 155-160”, a compound semiconductor of Cu2ZnSnS4 (Eg=1.39 eV) can be manufactured at a temperature of approximately 400° C. to 550° C. and exhibits p-type conductivity.
However, the compound semiconductor films of the above-described do not exhibit sufficient p-type conductivity. The manufacturing temperatures of the compound semiconductor films are high. Light emitting devices using the compound semiconductor films cannot obtain high intensity and may emit light only at a low temperature such as a liquid nitrogen temperature or a liquid helium temperature. It is known that the compound semiconductor of Cu2ZnSnS4 (Eg=1.39 eV) can be manufactured at the temperature of approximately 400° C. to 550° C. and exhibits the p-type conductivity, but the band gap thereof is narrower than an energy region of visible light. Therefore, when the compound semiconductor is laminated together with a light emitting material, light emitted from the light emitting material may be absorbed thereby.